A pneumatic tire has historically been sought which has a reliable means of retarding or stopping its deflation upon being punctured. Such a tire would reduce the frequency of tire changes on our high-speed interstate highways, thereby resulting in increased safety for the motoring public. Because attention to vehicle safety is on the increase, many vehicle and tire manufacturers have become interested in equipping vehicles with pneumatic tires having the capability of either sealing or reducing the rate of inflation loss after puncture. Some vehicle and tire manufacturers have become interested in equipping vehicles with such a tire in conjunction with a low-pressure warning device that would inform the motorist when the tire-inflation pressure drops below a prescribed amount and then the "slow-leak" feature of such a tire would allow the motorist to take corrective action.
Various approaches to achieve a sealant or "slow-leak" pneumatic tire have been proposed without lasting commercial success. One approach that has been proposed is to attach a layer of elastomer sealant containing no curatives to the inside of the unvulcanized tire. The tire is then vulcanized resulting in an unvulcanized sticky layer of elastomer on the inside of the vulcanized tire which acts as a sealant. This approach has not had significant commercial success because of manufacturing, technical, and economic problems associated with producing such a tire. The unvulcanized layer of elastomer sealant has a tendency to stick to the curing bladder thus causing high amounts of unacceptable tires. Even when an acceptable tire is produced by this method, during normal service of the tire other problems occur. Since the elastomer sealant is unvulcanized, it behaves like a plastic and will flow to the center of the tire as a result of the heat and centrifugal force generated by high-speed driving.
Another approach proposed to achieve a sealant or "slow-leak" tire is to apply a soft sticky sealant layer to the inside of a vulcanized tire. Although this approach solves the manufacturing problems discussed above, it creates a new set of problems. The inside of the tire must be thoroughly cleaned to remove the residual mold-release agent, usually by buffing, in order to obtain adhesion between the inside of the tire and the sealant. U.S. Pat. No. 3,935,893 describes a sealant added to a vulcanized tire and a cleaning technique used to obtain adhesion between the tire and sealant. Although effective, the cleaning process used for these types of sealants is time consuming and expensive. It is desirable to have a tire sealant which can be built onto an unvulcanized tire and vulcanized therewith.